1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly, to a manufacturing method of an array substrate for a liquid crystal display (LCD) device including a reflector.
2. Discussion of the Related Art
Due to the rapid development in information technology, display devices have evolved into instruments that can process and display a great deal of information. Flat panel display (FPD) devices, which have the properties of a thin profile, low weight and low power consumption, have been developed.
The FPD devices may be classified into two types depending on whether the device emits or reflects/transmits light. One type is a light-emitting type display device that emits light to display images, and the other type is a light-reflecting/transmitting type display device that uses an external light source to display images. Plasma display panels (PDPs), field emission display (FED) devices, and electroluminescent (EL) devices are examples of the light-emitting type display devices. Liquid crystal display (LCD) devices are examples of the light-reflecting/transmitting type display device.
Among many kinds of FPD devices, LCD devices are widely used for notebook computers and desktop monitors because of their excellent characteristics of resolution, color display and display quality.
In general, a liquid crystal display (LCD) device includes two substrates, which are spaced apart and facing each other, and a liquid crystal layer interposed between the two substrates. Each of the substrates includes an electrode and the electrodes of each substrate are also facing each other. Voltage is applied to each electrode and an electric field is induced between the electrodes. An arrangement of the liquid crystal molecules is changed by varying the intensity of the electric field. The LCD device displays a picture by varying the light intensity according to the arrangement of the liquid crystal molecules.
Because the LCD device is not luminescent, it needs an additional light source in order to display images.
Therefore, a backlight is arranged behind a liquid crystal panel and is used as a light source. Light incident from the backlight penetrates the liquid crystal panel, and the amount of light transmitted is controlled depending on the arrangement of the liquid crystal molecules. Here, the substrates are usually transparent and the electrodes of each substrate are usually formed of a transparent conductive material.
This LCD device is referred to as a transmissive type LCD device or a transmissive LCD device. Because the transmissive LCD device uses the backlight as a light source, it can display a bright image in dark surroundings. However, the transmissive LCD device has high power consumption due to the operation of the backlight.
To remedy this disadvantage, a reflective (or reflection type) LCD device is suggested. The reflective LCD device displays images by reflecting external light, thereby resulting in low power consumption as compared with the transmissive LCD device. In the reflective LCD device, a pixel electrode on a lower array substrate is made of a conductive material having high reflectance and a common electrode on an upper color filter substrate is made of a transparent conductive material so that external light can be transmitted therethrough.
However, the reflective LCD device cannot be used in dark surroundings because it depends on an external light source.
To solve the above problems, a transflective LCD device has been recently proposed and developed. The transflective LCD device can be used both in a transmissive mode and in a reflective mode. A related art transflective LCD device will be described hereinafter more in detail.
FIG. 1 is a cross-sectional view of an array substrate for a related art transflective LCD device. As shown in FIG. 1, a reflective area RtA and a transmissive area TmA, which together constitute a pixel area, are defined on a substrate 3.
In the reflective area RtA, a gate electrode 9 is formed on the substrate 3. Although not shown in the figure, a gate line and a storage electrode are also formed in the same layer as the gate electrode 9. A gate insulating layer 15 is formed on an entire surface of the substrate 3 including the gate electrode 9. A semiconductor layer 18 is formed on the gate insulating layer 15 corresponding to the gate electrode 9. The semiconductor layer 18 includes an active layer 18a and an ohmic contact layer 18b. 
A source electrode 21 and a drain electrode 24 are formed over the semiconductor layer 18. The source electrode 21 and the drain electrode 24 contact the ohmic contact layer 18b of the semiconductor layer 18. The source electrode 21 and the drain electrode 24 are spaced from and facing each other. The gate electrode 9, the semiconductor layer 18, the source electrode 21 and the drain electrode 24 constitute a thin film transistor Tr.
Next, a first passivation layer 30 is formed on the source and drain electrodes 21 and 24 and the active layer 18a exposed between the source and drain electrodes 21 and 24. Convex patterns 35 are formed on the first passivation layer 30 and a second passivation layer 37 covers the convex patterns 35 to have an uneven surface. The second passivation layer 37 has a drain contact hole 44 exposing the drain electrode 24 with the first passivation layer 30. The first passivation layer 30 is formed of an inorganic material and the second passivation layer 37 is formed of an organic material.
A reflector 41 is formed on the second passivation layer 37 by depositing a metal material that reflects light well. The reflector 41 also has an uneven surface due to the uneven second passivation layer 37. The reflector 41 is connected to the drain electrode 24 through the drain contact hole 44.
Meanwhile, in the transmissive area TmA, the gate insulating layer 15 and the first passivation layer 30 are sequentially formed on the substrate 3. The first passivation layer 30 is removed in the transmissive area TmA to expose the gate insulating layer 15 and to form a step between the transmissive area TmA and the reflective area RtA.
Next, a pixel electrode 49 is formed in the reflective area RtA and in the transmissive area TmA by depositing a transparent conductive material and then patterning it. The pixel electrode 49 contacts the reflector 41, and is electrically connected to the drain electrode 24.
FIGS. 2A to 2F show a manufacturing method of the array substrate for the transflective LCD device according to the related art.
Forming a switching element such as a thin film transister Tr, which includes a gate electrode, a semiconductor layer, a source electrode and a drain electrode, may use a conventional manufacturing method, and therefore, it will not be described in detail.
As shown in FIG. 2A, a first passivation layer 30 is formed on a source electrode 21 and a drain electrode 24 by depositing an inorganic material on an entire surface of a substrate 3 including a thin film transistor Tr as a switching element, wherein a reflective area RtA and a transmissive area TmA are defined on the substrate 3. The first passivation layer 30 improves adhesion between layers, but may be omitted. An organic layer 31 is formed on the first passivation layer 30 by coating a photosensitive organic material such as photo acryl.
Next, a mask 32 including light-blocking portions BA and light-transmitting portions TA is disposed over the organic layer 31 and a first mask process is performed. The organic layer 31 is exposed to light through the mask 32. Because the organic layer 31 is formed of the photosensitive organic material such as photo acryl, a process of forming a photoresist on the organic layer 31 can be omitted.
As shown in FIG. 2B, the exposed organic layer 31 is developed, and portions that are not exposed to light are removed to form organic patterns 33 in the reflective area RtA. At this time, an inclination angle of a convex pattern (to be formed later) may be changed by controlling a distance between the organic patterns 33. Here, the photosensitive organic material is a negative type, where a portion that is not exposed to light is removed. A photosensitive organic material of a positive type, where a portion that is exposed to light is removed, may also be used.
As shown in FIG. 2C, the substrate 3 including the organic patterns 33 of FIG. 2B is heat-treated, and thus convex patterns 35 are formed. Surfaces of the organic patterns 33 of FIG. 2B are melted through a heat-treatment process to spread out, and then is hardened resulting in the convex patterns 35.
As shown in FIG. 2D, a second passivation layer 37 is formed by coating the same organic material as the convex patterns 35 on an entire surface of the substrate 3 including the convex patterns 35. The second passivation layer 37 has an uneven surface, which has a proper inclination angle, due to the convex patterns 35 in the reflective area RtA and a flat surface in the transmissive area TmA.
Next, as shown in FIG. 2E, a second mask process is carried out and the second passivation layer 37 and the first passivation layer 30 are patterned. Thus, in the reflective area RtA, a drain contact hole 44 exposing the drain electrode 24 is formed, and in the transmissive area TmA, the second passivation layer 37 and the first passivation layer 30 are removed to form a step between the reflective area RtA and the transmissive area TmA.
A reflector 41 is formed on the second passivation layer 37 in the reflective area RtA by depositing a metal material that reflects light well and then patterning it. At this time, the reflector 41 also has an uneven surface due to the second passivation layer 37. The metal material is removed in the transmissive area TmA and thus there exists no reflector 41 in the transmissive area TmA. The reflector 41 contacts the drain electrode 24 through the drain contact hole 44 and functions as a reflective electrode.
As shown in FIG. 2F, a pixel electrode 49 is formed by depositing a transparent conductive material on the substrate 3 including the reflector 41 thereon and then patterning it. The pixel electrode 49 contacts the reflector 41 in the reflective area RtA and contacts a gate insulating layer 15 in the transmissive area TmA.
In the manufacturing method of the above array substrate, two mask processes are required for forming the uneven passivation layer. That is, the first mask process is performed for forming the convex patterns and the second mask process is carried out for forming the drain contact hole and the step between two areas in the second passivation.
The cost of materials may be increased because of twice coating an organic material. In addition, when the convex patterns are formed of a first organic layer and the second passivation layer is formed of a second organic layer over the convex patterns, the unevenness of the convex patterns may not be thoroughly reflected in the second passivation. Thus, the reflector may have a bad and uneven surface.